1. Field of the Invention
The present invention relates to a reflector and a displacement measurement apparatus using the reflector and, more particularly, to a reflector suitably used as a reflection beacon member (reflection target member), or reflection optical scale used for a photoreflector (photosensor), reflection encoder, or optical measurement device, or the like which includes a light source and light-receiving means and is used to detect the presence/absence of an object or a change in the object. In addition, the present invention relates to a displacement measurement apparatus such as a linear encoder or rotary encoder which detects displacement information such as a moving amount or moving speed by using an optical scale using the reflector.
2. Related Background Art
Various conventional photosensors using reflected light and encoders using the photosensors will be described with reference to FIGS. 46 and 47.
FIG. 46 is a schematic view of a reflection photosensor (photoreflector). FIG. 47 shows a photoreflector with a lens. FIGS. 48A to 48C show the edge response measurement arrangement (FIG. 48A) and characteristics (FIGS. 48B and 48C) of the photoreflector with the lens in FIG. 47. FIG. 48A shows a photosensor PS.
The arrangement shown in FIG. 47 includes a light source (LED) 101, a light-receiving portion (photodiode or phototransistor) 102, lenses 103 and 104, a detection object 105 for the detection of movement information or a displacement measurement target (reflection object 105), an aluminum reflection film 105a, a nonreflection portion 105c, and a substrate 105b. 
The reflection sensor PS shown in FIG. 47 irradiates the measurement/observation target (reflection object) 105 with a light beam from the light source 101 and detects a light beam from the reflection object 105 by using the light-receiving means 102, thereby determining/measuring the presence/absence of the reflection object 105, a difference in reflectance, and the difference between reflection and nonreflection (or absorption). A special reflection target is mounted on the measurement/observation object 105, as needed.
FIG. 49 shows an arrangement which can detect the movement information of the moving object 105 with high precision and resolution. A so-called reflection optical encoder or the like used, in which light from a reflection scale 105d obtained by periodically arraying reflection slits formed by reflection portions 105a and nonreflection portions 105c at a small pitch is detected by the light-receiving means 102 to count the number of bright and dark patterns of the reflection slits, thereby measuring the displacement of the moving object 105.
Various sensors and apparatuses are available, which irradiate the object 105 serving as a measurement or observation target with a light beam from the light source 101, and receive reflected light from a reflection target or reflection scale 105d mounted on the object 105 by using the light-receiving means 102, thereby detecting the presence/absence of the object or its moving state.
The above reflection sensor, the reflection target irradiated with a light beam from a light source in a reflection optical measurement apparatus or the like, and the reflector 105 having a reflection scale utilize the presence/absence of reflected light from a reflector, a difference in reflectance on the reflector, the difference between reflection and nonreflection (or absorption) on the reflector, and the like.
In general, a reflector uses an aluminum reflection film or metal reflection member at a desired reflection portion serving as a measurement/observation target. Alternatively, the surface of a reflection portion is formed by a mirror surface, and the surface of a nonreflection portion is roughened into a diffusion surface or the like.
FIG. 48B shows the relationship between the distance between the photosensor PS and the reflector 105 and the output current from the light-receiving element. FIG. 48C shows the relationship between an edge response characteristic, i.e., the edge migration distance of the reflector 105, and the output current from the light-receiving element.
A reflector that has an aluminum reflection film on a desired reflection portion serving as a measurement or observation target on an object to improve the reflectance is an effective means for detecting movement information because a sufficiently large reflected light intensity difference can be set between the reflection portion and the nonreflection portion. However, it is difficult to form an aluminum deposition film as a reflector on a substrate. In addition, in a high temperature/high humidity environment, the aluminum film tends to peel off. This poses a problem in terms of reliability.
Furthermore, when an aluminum reflection film is used as a reflector, a high reflectance can be expected, and a sufficiently larger reflectance difference can be realized between a reflection portion and a nonreflection portion. If, however, it is combined with the conventional reflection photosensor shown in FIG. 47, the reflector cannot guide a sufficient amount of light beam to the light-receiving element 102 when the light beam is returned to the light source side. Therefore, this arrangement tends to lack in absolute light amount. If this problem is to be avoided by increasing (enhancing) the emission intensity of the light source 101, the power consumption of the light source increases.
In the photosensor PS shown in FIG. 47, in order to solve such problems, the lens 103 is placed on the light source 101 side to increase the light irradiation intensity for the reflector 105 per unit area, and the lens 104 is also placed on the light-receiving portion 102 side to guide a widely divergent light beam reflected by the reflector 105 to the small light-receiving surface.
In the reflection sensor having lenses mounted on the light-emitting portion 101 and light-receiving portion 102, respectively, the photosensor PS must be assembled while the ideal positional relationship geometrically/optically determined by the light-emitting element 101, lenses 103 and 104, reflector 105, and light-receiving element 102 is maintained. In addition, in the combination of the reflector 105 and the photosensor PS, in order to obtain a high optical transmission efficiency between light emission and light reception, the reflection posture (reflection angle, the distance from the sensor, and the like) of the reflector 105 must be maintained to a predetermined positional relationship with high precision. The thickness of the photosensor PS itself increases due to the use of lenses. This hinders reductions in the size and thickness of the apparatus.